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Calculating [OH-] from kw

  1. Mar 23, 2012 #1
    So I thought if I have the value of Kw and I need to find the concentration of [OH-] then all I would have to do is square root the Kw. But in this example, it is not the case why?

    Kw at 50oC is 5.48x10-14. Calculate OH- concentration

    so i just square rooted 5.48x10-14 and got 2.34 x10-7. Shouldn't this be right?
  2. jcsd
  3. Mar 23, 2012 #2


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    Staff: Mentor

    For a pure water at 50°C that would be a correct approach. Is there some additional information in the question?
  4. Mar 24, 2012 #3
    No. It just states "calculate the [OH] concentration from the above solution at 50 degrees" But, I am pretty sure that would not make a difference. Correct?
  5. Mar 24, 2012 #4
    What is "the above solution"?
  6. Mar 25, 2012 #5
    Kw= [H+][OH-] by definition.
    If [H+]=[OH-] then [OH-]=Sqrt (Kw)
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